The objectives are: (1) to identify specific chromophores of near-ultraviolet irradiation (NUV) that lead to biological alterations; (2) to identify photoproducts; (3) to identify the macromolecular changes produced by the photoproduct (e.g., DNA breaks, DNA-protein crosslinks); (4) to establish the relative importance of each macromolecular change; (5) to determine the mechanism of repair of biological damage; (6) to identify the specific alterations that account for mutation by NUV (above 300nm) and by photoproducts (i.e., base pair change, transition, transversion, frameshift, deletion, genetic recombination); (7) to test whether NUV results in the induction of DNA metabolism enzymes, as has been found for far (254nm) UV, and for nitrosoguanidine; (8) to test whether NUV (alone and synergistically) interferes with DNA replication and repair in eukaryotic cells; (9) to test abiotic effects of NUV under realistic (i.e., solar and industrial lamp) conditions, tests should be able to identify changes upon long expose with low doses; (10) to establish a testing scheme that would be particularly suitable for research with NUV and various photoproducts under conditions of low dosage but long exposures.